1. Field of the Invention
The present invention relates to an image encoding system which encodes an image signal.
2. Description of the Related Art
FIG. 22 is a block diagram of a conventional image encoding device which is disclosed in, for example, a recommendation H.261 made by the International Telegraph and Telephone Advisory Committee ITU-T. In this image encoding device, an input image signal 201 is input into a differentiator 202; the differentiator 202 finds a difference between the input image signal 201 and a predictive signal 203 (which will be discussed later), and outputs a signal representing the difference as a predictive error signal 204; on receiving the predictive error signal, an orthogonally transforming part 205 transforms it from a space area to a frequency area and outputs the result to a quantizer 206; and, the quantizer 206 quantizes the outputs of the orthogonally transforming part 205 linearly, and then outputs the linearly quantized outputs as quantized data 207.
The quantized data 207 generated by the quantizer 206 is then diversified into two sections, one of which is encoded so that it can be transmitted to a receiving side. That is, one section of the quantized data 207 is encoded in an encoding part 209 in accordance with a table held in an encoding table 208, thereby providing encoded data 210. The other section of the quantized data 207 is reversely quantized in a reverse quantizer 211 and the result thereof is output to a reversely orthogonally transforming part 212. The reversely orthogonally transforming part 212 transforms the output of the reverse quantizer 211 from a frequency area to a space area and then outputs the result as a decoded predictive error signal 213 to an adder 214. The adder 214 adds the decoded predictive error signal 213 to the predictive error signal 203 to thereby obtain a decoded image signal 215, and then outputs the decoded image signal 215.
The decoded image signals 215 are stored collectively in a memory 216 such as a frame memory or the like. The memory 216 delays the decoded image signal stored therein and then outputs it as the decoded image signal 217 of a former frame to a predictive part 218. The predictive part 218 makes a motion compensation prediction by use of the input image signal 201 to be encoded and the frame delayed decoded image signal 217, and outputs the predictive signal 203 and a motion vector 219. The motion vector 219 is encoded by the encoding part 209, while the predictive signal 203 is transmitted to the above-mentioned differentiator 202 and adder 214.
However, since a conventional image encoding system is structured, for example, in the above-mentioned manner, it is difficult to encode an image signal in such a manner that the characteristics of the image signal are taken into proper account. Also, in the encoding part 209, generally, the image signals are encoded using a variable-length code but it is difficult to encode the image signals in such a manner as is best suitable for the incidence probabilities of the respective image signals. Further, when a plurality of target images to be encoded are present in an input image, it is impossible to perform individual encoding processings on the respective target images. Still further, it is also impossible that the target images are extracted from an input image and the extracted target images are encoded respectively using different encoding techniques to thereby build up a new image.